Microfabrication of Transition-Edge Sensor Arrays of Microcalorimeters with Ho-163 for Direct Neutrino Mass Measurements with HOLMES

HOLMES is aiming at a direct measurement of neutrino mass by performing a calorimetric measurement of the energy released in the decay of Ho-163. In such approach, the Ho-163 source, with the required activity, needs to be embedded in the detector. HOLMES will deploy a large array of transition-edge sensor microcalorimeters with implanted Ho-163 ions. While good progress has been made in optimizing single pixel design and fabrication to achieve the target resolution, a major challenge is the fabrication of arrays of such microcalorimeters with the required amount of Ho-163 ions embedded in the detectors absorber. We describe the multi-step microfabrication process implemented to produce the detector arrays for HOLMES. One crucial part of such process is the ability to perform co-deposition of gold during the Ho-163 implantation process on the detectors absorber. We describe the UHV target chamber, with integrated gold deposition system, we have built to achieve this goal.